Specific mutagens reproducibly activate specific oncogenes in a specific tissue. Resulting tumors often show the oncogene to have a specific mutation at one particular nucleotide position. The reproducible mutation may be due to this nucleotide position being either modified frequently or misrepaired frequently. We developed a novel technique, the Ligation Mediated-Polymerase Chain Reaction, to map alkylated adducts and ultraviolet light induced adducts in vivo at the nucleotide level of resolution on sequencing gels; even repair rates were quantified at nucleotide resolution. With this discovery, we will relate reproducible hot spots for oncogene activation to hot spots for adduct formation or to slow spots for adduct repair. Technology for mapping adduct frequency will be tailored to other alkylating agents, and to benzopyrene, dimethyl-benzanthracene, and aflatoxin, mutagens responsible for oncogene activation. Results from adduct mapping of p53 and several ras and myc oncogenes in murine tissue culture systems will be applied to mouse model systems.